1. Field of the Invention
The present invention relates to a method of controlling the charge rate of a nickel-cadmium (Ni-Cad) battery charger installed in a computer system.
2. Description of the Related Art
Some computer systems use a Ni-Cad battery to provide the power to the computer when an alternating current (ac) outlet is inconvenient or unavailable. The Ni-Cad battery is eventually drained and an ac power source is necessary to run the computer and/or recharge the Ni-Cad battery. The computer uses a Ni-Cad battery charger which controls the energy supplied during charging of the Ni-Cad battery.
Many techniques are available to charge Ni-Cad batteries. The quickest method is to charge the battery at a very high rate until it is fully charged and then to switch into a very slow rate, or trickle rate, to maintain that charge. The rate of charge depends upon the amount of current forced through the battery. A fast charge uses a high amount of current and a slow charge uses a relatively low amount of current. A Ni-Cad battery used in computers conventionally contains one or more individual Ni-Cad cells. The amount of current used to determine the charge rate depends upon the number of cells in the battery, the state of the cells in the battery, the power rating of each cell and other characteristics of the particular cells.
Ni-Cad batteries require special handling and control during fast charging to prevent overheating and damage. The battery charge controller must contain adequate monitoring devices and circuitry to charge the Ni-Cad battery at different rates, to detect the status of parameters such as voltage and temperature of the battery, especially at higher rates of charge, and to switch from one charge rate to another. Additionally, if the Ni-Cad battery is deeply discharged, if a fast charge is supplied, the battery may draw too much energy and interfere with computer operation by drawing down the voltage. The battery charge control circuitry must also compensate for this condition. Battery chargers may, therefore, require complex circuitry as well as expensive components to achieve these tasks.